Adsorption-based gas separation plants (e.g., pressure swing adsorption (PSA) systems or vacuum pressure swing adsorption (VPSA) systems) operate at various capacities. There has been and continues to be an increased demand for such plants to have higher product throughput. One way to achieve this goal is to increase the plant size, as current trends for these large tonnage plants become commercially more cost effective.
Large tonnage VPSA plants require increased blower size and/or speed. Increasing the blower size, however, also increases radiated noise and pulsations levels in the plant. Such pulsations may lead to pipe vibrations that can ultimately damage pipes, beds or other equipment such as an aftercooler in the plant. In addition, noise generated by these pulsations could be dangerous for the safety and health of plant personnel and the environment. For example, the sound pressure level at the exit of a typical large size vacuum blower can reach levels up to about 170-180 dB. For safety, environmental and/or regulatory concerns, however, the sound pressure level needs to be reduced to about 90 dBA.
To reduce pulsation, and hence the dissipated noise by the discharged gas, VPSA plants typically employ a silencer at the discharge of the vacuum blower. Current noise silencing in standard VPSA plants is provided by commercially available cylindrical steel-shell type silencers. As these silencers become larger both in length and diameter to provide the necessary sound attenuation for larger plants, they become more prone to vibrate, act as a noise source and can fail mechanically. The cost to manufacture and maintain such silencers therefore increases. Because of economics, reliability and effectiveness, steel-shell silencers do not scale-up successfully for large tonnage plants. This requires an alternative method of silencing blower noise in such plants.
U.S. Pat. No. 6,089,348 to Bokor and U.S. Pat. No. 4,162,904 to Clay et al. exhibit typical industry practice for silencing blower noise. In both of these patents, it is suggested that the blower noise can be reduced or dissipated by a steel-shell type cylindrical silencer that include multiple chambers. These types of silencers become ineffective for large blowers that generate high levels of pulsations as their shell vibrates due to blower pulsations. In addition, the cost to manufacture and maintain such silencers is adversely affected by increased blower size. Consequently, these silencers do not scale up economically for large plants.
U.S. Pat. No. 5,957,664 to Stolz et al. suggests the use of a Helmholtz resonator type pulsation dampener in the discharge conduit of the blower just before the silencer so that pulsation entering into the silencer can be dampened, and hence the performance of the silencer can be improved. Such an approach is limited, however, given that the design of such resonators is only effective at a given frequency for a specified design condition. In many instances, blowers generate pulses not only at a single frequency, but also at its harmonics.
U.S. Pat. No. 6,451,097 to Andreani et al. presents an alternative approach to attenuation of blower noise by disclosing a partially buried structure. This structure has impedance tubes and baffles to provide noise attenuation.
In view of the prior art, it would thus be desirable to provide more reliable, cost effective, and better performing silencers for use in adsorption-based gas separation plants.